1. Field of the Invention
The present invention relates to irrigation systems, and more particularly to control systems therefor controlling the translation of moving irrigation pipes.
2. Description of the Prior Art
Agricultural irrigation, both because of statutory scheme and economic considerations, is best done in large tracts often in 160 acre increments. These large sizes dictate large irrigation arrangements which entail substantial lengths of irrigation pipe translated over the irrigated terrain to conserve equipment cost. In further contemplation of cost the irrigation pipe is designed for minimum weight and therefore includes thin walled segments supported at various points for translation.
Often the foregoing pipe structure is mounted for pivotal translation typically known as a center post irrigation system and may include sequenced end deployment, such as that described in our prior U.S. Pat. No. 4,033,508, to irrigate corners. Alternatively linearly translated pipe arrangements may be used in each instance the weight constraints on the pipe resulting in highly flexible and fragile structures which are translated over tilled ground. The foregoing translation is achieved by various powered dollies which also serve as the incremental pipe supports and it is the power variations and variations in the terrain that produce the major load deflections in the pipe.
Heretofore the pipe deflections of the foregoing type were corrected by various control systems responding to signals from mechanically coupled transducers such as strain gauges. Strain gauge use requires intimate contact with the pipe, thus subjecting the sensor to the temperature variations of the irrigation water. Similarly other mechanically coupled sensors respond to temperature effects, with the compounding effects of flexure modes being included in the sensor information. Furthermore most if not all prior art sensor arrangements entail the measurement of pipe deformation which because of cross coupling includes the loads due to vertical terrain undulation, a load input over which no control is possible or desired. For these reasons and others most of the prior art augmentation systems entailed elaborate control arrangements with the attendant cost and complexity in use. Furthermore load deflection sensing is typically pipe referenced and provides an inaccurate source of pipe position signals for possible program use.